Sequencing algorithms for multiple arc-welding robots considering thermal distortion

This paper focuses on sequencing welding lines in multiple arc-welding robot systems, which is the problem of assigning individual welding operations to robots as well as determining their sequences with the objective of minimizing the maximum completion time. Each welding operation is denoted by a weld line with two end-points, each of which can be a possible starting point for the welding operation. Thermal distortion is explicitly considered by introducing a delay between welding operations associated with weld lines near each other. Due to the complexity of the problem, this paper suggests three types of search heuristics, genetic algorithms, simulated annealing and tabu search, each of which incorporates new methods to generate neighbourhood solutions. To show the performances of the heuristics, computational experiments are performed on a number of randomly generated test problems, and the results are reported. In particular, some of the search heuristics outperform the exiting method.     

Sensitivity and validity of visual search models for multiple targets

This study proposes two search models for multiple targets (random search and systematic search) in an unstructured search field, derived by generalizing search models for single target search. Whilst the probability of locating a single target in the random search model is typically exponentially distributed, the probability of locating multiple targets was found to be distributed hypo-exponentially. The systematic search model was extended from a piecewise-linear function for a single target to a piecewise-curve function for multiple targets. To test whether these search models could predict human search performance, first, visibility area in a fixation, a main component of search models, was investigated at various fixation durations. Sensitivity analysis of this data indicated that using short fixation duration and a small fixation overlap would produce better search performance. Next, the visibility area data was combined with the search models and compared to human performance on a free search field with three targets. The systematic and random models provided upper and lower boundaries of actual human search performance. Additionally, at the start of the search task for multiple targets, search performance was close to the systematic search model, while for late targets, performance approached the random search model. Observers may have changed their search strategy during this multiple-target visual search task.     

Controlling asynchronous team design environments by simulated annealing

An organizational strategy for design environments,asynchronous teams, is reviewed. Simulated annealing is used to implement the necessarycontracting search behavior of asynchronous teams. An example of an asynchronous team design environment controlled by simulated annealing is given from the building design domain. The simulated annealing algorithm used, which has been modified for distributed use and multi-criteria, non-preference objectives, is described.     

Effect of pulse-current heating multiple forging on mechanical properties of Mg–Nd–Zn–Zr alloy

The effects of pulse current heating on microstructure evolution and mechanical property of Mg–Nd–Zn–Zr magnesium alloy during multiple forging are investigated. The results of uniaxial tensile test show that tensile strength, yield strength and elongation of the alloy are improved with the increasing of forging passes. Moreover, under the condition of pulse current heating, this promotion effect is more obvious. The results of microstructure analysis show that recrystallisation occurs during the deformation, and the recrystallisation is obviously accelerated by pulse current. The magnesium alloy billet with fine grains is obtained eventually. Theoretical analysis shows that pulse current can increase the recrystallisation nucleation rate and reduce the rate of grain growth, which is helpful to refine the grains of alloy.     

The Aesthetics of Politics in the Hungarian Photobook From Our Lives

Lajos Kassák is best known outside of Hungary for his commitment to international dialogue among the avant‐gardes of the late 1910s and early twenties, as exemplified by his periodical Today (Ma). Within Hungary, however, he is also recognized for his politically driven activities during the late twenties and early thirties, and specifically, for his role in organizing and promoting the leftist activities of the Work Circle (Munka Kör). The present essay challenges this traditional characterization of Kassák's career trajectory. A careful investigation of the paragon Work Circle project – the photobook From Our Lives (A Mi Életünkbo?l) – demonstrates that Kassák's sustained interest and commitment are neither to purely aesthetic nor to purely political goals, but rather, to the very notion of art's aesthetic potential for political impact. Once we recognize that From Our Lives is a pedagogic project, we can properly understand its impact on the Hungarian worker photography movement: it was essentially an instruction manual for artists on how to construct a socially conscious image. As such, it should be distinguished from other more political works which did indeed serve as showcases for exemplary worker photographs – and even from the explicitly political messages presented in the eponymous exhibitions with which the Work Circle photobook is often mistakenly conflated. The broader applicability and implications for this sort of pedagogic analysis of a work's form and function are discussed.     

A fuzzy AHP evaluation model for buyer–supplier relationships with the consideration of benefits,opportunities, costs and risks

With increasingly fierce global competition, firms in various industries need to build a cooperative buyer–supplier relationship to survive and to acquire reasonable profit. Even though the literature on various types of collaboration between firms is abundant and the works on supplier selection models are numerous, the research that provides a mathematical model for the selection of the most appropriate form of buyer–supplier relationship is very limited. Existing buyer–supplier evaluation models usually only consider the benefits from the relationship, but not the opportunities, costs and risks that may need to be confronted. The main objective of this study is to propose an analytical approach to evaluate the forms of buyer–supplier relationship between a manufacturer and its supplier. A fuzzy analytic hierarchy process (AHP) model, which applies fuzzy set theory and the benefits, opportunities, costs and risks (BOCR) concept, is constructed to deal with uncertainty and to consider various aspects of alternatives. Multiple factors that affect the success of the relationship are analysed by incorporating experts’ opinions on their priority of importance, and a performance ranking of the buyer–supplier forms is obtained. A case study of selecting the most appropriate buyer–supplier form between a TFT-LCD manufacturer and its colour filter supplier is presented, and the proposed model is applied to facilitate the decision process. The proposed model is a general form that can be tailored and applied by firms that are making decisions on buyer–supplier relationship.     

Evaluation of crack growth behavior and probabilistic S–N characteristics of carburized Cr–Mn–Si steel with multiple failure modes

The unexpected failures of case-hardened steels in long life regime have been a critical issue in modern engineering design. In this study, the failure behavior of a carburized Cr–Mn–Si steel under very high cycle fatigue (VHCF) was investigated, and a model for evaluating the probabilistic S–N curve associated with multiple failure modes was developed. Results show that the carburized Cr–Mn–Si steel exhibits three failure modes including the surface flaw-induced failure, the interior inclusion-induced failure without the fine granular area (FGA) and the interior inclusion-induced failure with the FGA. As the predominant failure mode in the VHCF regime, the interior failure process can be divided into four stages: (i) the small crack growth around the inclusion, (ii) the stable macroscopic crack growth outside the FGA, (iii) the unstable crack growth outside the fish-eye and (iv) the momentary fracture outside the final crack growth zone. The threshold values are successively evaluated to be 2.33 MPa m^1/2, 4.13 MPa m^1/2, 18.51 MPa m^1/2 and 29.26 MPa m^1/2. The distribution characteristics of the test data in transition failure region can be well characterized by the mixed two-parameter Weibull distribution function. The developed probabilistic S–N curve model is in good agreement with the test data with multiple failure modes. Although the result is somewhat conservative in the VHCF regime, it is acceptable for safety considerations.     

螺栓连接结构冲击载荷传递特性及冲击响应行为研究进展综述

目的 通过探讨复杂装备结构中螺栓连接结构在冲击载荷条件下的力学响应特征,以及这些特征如何影响装备结构的应力波传播、能量耗散和整体结构响应;同时,关注螺栓自身的变形和破坏对关键部件乃至整个系统稳定性和安全性的潜在影响,特别是在武器装备中可能引发的灾难性后果,旨在进一步优化螺栓连接结构的设计,提高其在极端载荷条件下的性能和可靠性。方法 系统调研国内外文献,总结螺栓连接结构冲击载荷传递特性及冲击响应行为的研究进展,涉及的研究方法包括试验研究、有限元模拟和理论分析等。结论 螺栓连接结构的冲击响应行为对装备整体的稳定性和安全性具有重要影响。通过对现有文献的分析,提出了未来研究的建议。     

Ermakov album

Abstract

When I first met Henry Ries in his home in Manhattan in the mid-1980s, I was struck by his generosity in telling me about his career. Born in 1917 in Berlin-Wilmersdorf in an assimilated Jewish family, Henry (born Heinz) Ries left for New York on 13 January 1938. Initially, he found employment in Bridgeport, Connecticut, where he taught photography at the Jewish community centre and could use their laboratory for his own work. He tried to enlist in the United States Army in December 1941, but this was not possible, since he was an 'enemy alien' and a recent emigrant without American citizenship. In May 1943, he joined the Army Air Corps and received American citizenship. Initially posted to the Pacific theatre, making aerial photographs of China for the 20th Bomber Command, he subsequently transferred to the European theatre, arriving in London in late May 1945. Assigned to the ‘Office Director of Intelligence’, his first job was to evaluate Heinrich Himmler's ‘secret state library’ correspondence with the SS, Hitler, Goebbels, Goring, and others, which was later utilized in the Nuremberg Medical Trial. Three months later, Ries was transferred to Berlin.     

Manuel González Salazar,the Peruvian Atget

The Lima-born photographer Manuel González Salazar documented the colonial architectural heritage of his native city, as well as other major Peruvian cities such as Cusco, Arequipa, Ayacucho, Cajamarca and Trujillo. Just as Eugène Atget had documented the old Paris that he saw gradually disappearing, González Salazar chose to photograph the architectural and artistic heritage of the colonial era, which dominated the urban environment of the Peru of his day, but which was threatened by modernisation and social change. Like Atget in the French context, González Salazar is an anomaly in the history of Peruvian twentieth-century photography, which is best known on the international stage for indigenismo and the depiction of pre-Hispanic customs. The rediscovery of González Salazar’s work invites scholars to pay greater attention to the cultural heritage of the colonial era, as well as to the archives that documented it in all its splendour.